1. Field of the Invention
This invention relates to fibers which are primarily para-aramid and preferably poly(p-phenylene terephthalamide) (PPD-T) and which include, as a spun-in additive, polyvinylpyrrolidone (PVP). The fibers, with the blend of para-aramid and PVP, exhibit tensile properties which are improved over those of fibers made from para-aramid, alone; and the fibers with the blend exhibit a variety of additional benefits such as, improved dyeability, increased stability to ultraviolet radiation, improved strength retention after heat aging, increased adhesion in composite structures, improved flame resistance, and the like.
2. Description of the Prior Art
European Patent Application No. 248,458, published Dec. 9, 1987 on the application of Maatman et al., discloses fibers made from a blend of PPD-T and another aromatic polyamide.
U.S. Pat. No. 4,224,271, issued Sept. 23, 1980 on the application of Tse, discloses preparation of fibers using an aromatic polyamide and polyacrylonitrile.
U.S. Pat. No. 4,278,779, issued July 14, 1981 on the application of Nakagawa et al., discloses fibers of improved dyeability made from a blend of poly(m-phenylene isophthalamide) and another aromatic polyamide.
U.S. Pat. No. 4,622,265, issued Nov. 11, 1986 on the application of Yoon et al., discloses fibers made from a blend of PPD-T and a regularly ordered aromatic-aliphatic copolymer.
U.S. Pat. No. 4,721,755, issued Jan. 26, 1988 on the application of Maatman, discloses fibers made from a blend of PPD-T and a polyamide containing diaminobenzanilide units.
U.S. Pat. No. 4,228,218, issued Oct. 14, 1980 on the application of Takayanagi et al., discloses a polymeric composite of a polymer having a rigid molecular structure uniformly dispersed in a polymer having a flexible molecular structure.
U.S. Pat. No. 3,869,429, issued Mar. 4, 1975 on the application of Blades, discloses, generally, that polyamides can be blended with as much as 30 percent of a compatible diluent polymer which should be reasonably stable and soluble in the dope solvent.
Japanese Patent Application Publication (Kokai) 55/69,621, published May 26, 1980, discloses the use of polymers having an affinity with carboxyl groups in polyamide polymerization processes. The polymers having an affinity with carboxyl groups include polyvinylpyrrolidone. The polyvinylpyrrolidone of that publication is used only during the polymerization and is carefully and completely removed before use of the polyamide polymer product.